We have an assembly with several bits of hardware (capscrews, washers & hex nuts) of various sizes and applications.  When the file is closed one day, then opened the next day, some the hardware changes what it is.  For example, capscrews are becoming hex nuts, hex nuts are becoming capscrews, etc.  The "Part" file of the capscrew has several configurations of the same fastener size.  3/8" part has serveral different lengths and styles, as well as the hex nut part has several different styles.

Why would SolidWorks allow a part to change to a "different" part within an assembly when pulling up the assembly or even while working within an assembly?  Do we have a corrupt file or work station?  Has the ghost of SW past come to visit?

We have never seen this happen.  We have seen configurations (within a part) change while working in an assembly, but never to another part.